The present invention relates to non-thermal pasteurization and/or sterilization of a living-mammal-instillable liquid to destroy live pathogens living in the liquid.
Various methods of pasteurizing liquids such as liquid foods, fermentation broth, biological fluids, blood products, medicines, vaccines, etc., have been used for destroying live pathogens, including bacteria, viruses and fungi, living in the liquids. However, these methods typically generate heat during the pasteurization process and may also introduce impurities depending on the process. This heat can easily damage active components, ingredients or other desirable characteristics of the liquid, such as food nutrients and sensory attributes, including flavors, aromas and colors. If these products are thermally processed, they will become unacceptable or their commercial values will be greatly reduced. In the case of biological fluids living cells may be altered or damaged. Therefore, a number of minimal thermal processes have been developed for some of these applications, including ultra-filtration, ozonation, pulsed ultraviolet light, irradiation, high hydrostatic pressure (HHP) and pulsed electric field (PEF) discharge.
Of these methods, PEF discharge has been shown to be very effective for killing bacteria within liquids. PEF discharge is considered to be one of the premier new technologies with a great potential of replacing thermal, chemical and other pasteurization and sterilization technologies for the treatment of liquid foods and pharmaceuticals. However, there are a number of drawbacks of the PEF discharge technology. For example, ohmic heating occurs during the PEF discharge, which causes the temperature of the liquid being treated to rise. Hence, a cooling system must be used in order to maintain the liquid at a low temperature. A significant amount of energy is wasted with unwanted heating and cooling of the liquid. Also, the requirement of a cooling system adversely increases the time required to treat the liquid. In addition, the PEF electrodes are immersed directly in the liquid. Since the electrodes contact the liquid, they are regarded as a major contamination source to the liquid due to oxidation of the electrodes during discharge. The electrodes must therefore be replaced regularly, which increases maintenance time and costs.
Improved methods of non-thermal pasteurization are desired for pasteurizing liquids without degrading the natural characteristics of the liquids.
One aspect of the present invention is directed to a method for at least partially sterilizing a liquid that has pathogens living in the liquid. The method includes placing the liquid comprising living pathogens in a reaction volume, and generating a non-thermal plasma within the reaction volume to thereby kill at least a portion of the pathogens within the liquid.
Non-thermal plasma species are generated by applying a high voltage, low current charge between two opposite polarity electrodes. The non-thermal plasma species often include electrically neutral gas molecules, charged particles in the form of positive ions, negative ions, free radicals and electrons, and quanta of electromagnetic radiation (photons). These non-thermal plasma species are highly reactive and are effective in killing live pathogens, such as bacteria, viruses and fungi, living in the liquid being treated.
Another aspect of the present invention is directed to a liquid food pasteurization apparatus. The apparatus includes a liquid food input, a treatment flow path coupled to the liquid food input, a pump, a gas injector and a non-thermal plasma reactor. The pump is coupled to the treatment flow path for pumping liquid food from the liquid food input through the treatment flow path. The gas injector is coupled in the treatment flow path and has a gas inlet for receiving a gas to be injected into the liquid food. The non-thermal plasma reactor is also coupled in the treatment flow path and includes a liquid food inlet, a liquid food outlet, a reaction volume between the liquid food inlet and the liquid food outlet, and at least one non-thermal plasma electrode adjacent to the reaction volume. Each non-thermal plasma electrode is isolated physically and electrically from the flow path by a dielectric barrier.
Another aspect of the present invention is directed to a liquid food pasteurization apparatus, which includes a liquid food input, a gas source and a non-thermal plasma reactor. A liquid food comprising living pathogens is received through the liquid food input. Gas bubbles are introduced from the gas source into the liquid food received from the liquid food input to produce a mixture of the liquid food and the gas bubbles. The non-thermal plasma reactor receives the mixture of the liquid food and the gas bubbles within a reaction volume and generates a non-thermal plasma within the reaction volume to thereby kill at least a portion of the pathogens within the liquid food.